Modifying plot appearance

Everything here is purely about display — it changes how your results look on screen (and in exports), not the underlying data.

Open via Plot → Modify plot appearance (Ctrl+M).

PIVlab Modify plot appearance panel — The **Modify plot appearance** panel.

Vector appearance

Control	Effect
autoscale vectors	Automatically scales vector length for readability.
Vector scale	Manual scale factor (default 5), used when autoscale is off.
Vector line width	Thickness of the drawn vectors (default 0.5).
plot every nth vector, n =	Shows only every nth vector — useful when the field is too dense to read (a wavelet-optical-flow analysis, for example, produces one vector per pixel).
hide vectors	Hides vectors entirely — useful when you only want to show a derived-parameter overlay.
uniform vector scale	Draws every vector at the same length, regardless of velocity — direction only. Pairs well with magnitude coloring.
power law vector scale	Scales vector length with a sublinear power function instead of linearly — long vectors are compressed more as the exponent (default 0.3) gets smaller, so a few very fast vectors don't visually dominate the plot.

Background image

The Background dropdown chooses what's shown behind the vectors: Display PIV image, Solid black, or Solid white. Enhance PIV image display (on by default) improves the raw image's contrast purely for display.

Vector colors

Four colors, each chosen from a preset list:

Role	Default
Valid (1st peak)	The primary color for good vectors. Can also be set to Magnitude — see below.
Valid (2nd peak)	Vectors taken from the correlation's second peak.
Replaced / interp.	Vectors that were rejected and filled by interpolation.
On derivatives	Vector color when a derived parameter (e.g. vorticity) is shown underneath.

These are the colors validation uses The colour legend shown on the velocity-based and image-based validation panels reflects exactly these four settings.

Coloring vectors by velocity magnitude

Setting Valid (1st peak) to Magnitude colors each arrow by its own velocity, using the Color map chosen further down the panel. A colorbar appears if Show colorbar is set to a position, labelled in m/s if the data is calibrated, otherwise px/frame.

Side-by-side comparison of a vortex-pair vector field: the left panel draws every arrow in flat green, the right panel colors each arrow by its velocity magnitude with a colorbar — A flat vector color (left) and Magnitude coloring (right).

It combines well with uniform vector scale: length then shows direction, color shows speed.

The same vortex-pair field drawn with uniform vector scale so all arrows are equal length, with color still encoding velocity magnitude — uniform vector scale combined with Magnitude.

All vectors are colored — 2nd-peak and interpolated included. Switch back to a flat color when you need to see which vectors were replaced.
Not available over a derived parameter: the vector color then comes from On derivatives, which has no Magnitude entry.
The color range is re-fitted to each frame, so a color does not mean the same speed in two different frames — read the colorbar when comparing.

Also here: Mask transparency [%] (default 50) — controls how see-through the red overlay is when viewing masks.

Derived-parameter colormap

Control	Effect
Colormap opacity [%]	Transparency of the derived-parameter overlay (default 75).
Color map	Parula, HSV, Jet, HSB, Hot, Cool, Spring, Summer, Autumn, Winter, Gray, Bone, Copper, Pink, Lines, or Plasma.
Steps	Number of discrete colors in the map (256 down to 2).
Image interpolation	bilinear (default), bicubic, or nearest — how the colormap image is resampled for display.

A velocity-magnitude overlay drawn with a small number of discrete colour steps, giving banded contours instead of a smooth gradient — The same field with a low number of colour Steps — the map becomes banded, turning a smooth gradient into discrete contour-like levels.

Color legend

Control	Effect
Show colorbar	None, or a position: South/North/East/West Outside.
Colorbar numeric format	Compact notation, scientific notation, or fixed-decimals.

Reference vector

A reference vector is a fixed-length arrow drawn in a corner of the plot so viewers can judge scale at a glance. Set its Reference vector scale (in the same units as your vectors) and its position — Off, or one of the four corners.

Applying

Click Apply to refresh the display with your changes.